xii TRANSLATORS INTRODUCTION 



idioplasm of the same or of a lower order. And here 

 we come round again to the original observations 

 from which Weismann set out. For he found that 

 among the Hydrornedusae, although the sexual 

 cells seemed to arise in very different topographical 

 positions, there had always been a migration to 

 these localities of a material which he would now 

 call the germplasm. And here also, that the point 

 may be made plain, there may be mentioned the 

 observations of surgeons and physicians, who insist 

 that the growths of disease always conform strictly, 

 in their cellular nature, to the tissues from which 

 they arose, and that in the healing of wounds like 

 only grows from cellular like. 



Dr. Oscar Hertwig is a scientific naturalist of the 

 very first rank, and his name is peculiarly asso- 

 ciated with many of the most important advances 

 in our knowledge of cells and of embryology. To 

 him chiefly, for instance, is due the discovery of the 

 intimate nature of fertilisation that it consists in 

 the union of the nuclear matter of a cell from the 

 male with the nuclear matter of a cell from the 

 female. With the exception of Francis Balfour, no 

 man has laboured more patiently, or achieved more 

 wonderful results, in the investigation of the origin 

 and marshalling of cells by which the egg changes 

 into the adult. From his own experience, and from 

 his study of the observations made by others, he 

 has been led to doubt the validity of apparently 

 fundamental parts of Weismann's conception. In 

 the first place, he thinks that there is no evidence 

 for the existence of differentiating as opposed to 



